Explanation:
How do we know that dark matter isn't just normal matter exhibiting strange gravity?
A new observation of
gravitationally magnified
faint galaxies far in the distance behind a massive cluster of galaxies is
shedding new dark on the subject.
The above detailed image from the
Hubble Space Telescope
indicates that a huge ring of dark matter likely exists surrounding the
center of CL0024+17 that has no normal matter counterpart.
What is visible in the
above image, first and foremost,
are many spectacular galaxies that are part of
CL0024+17 itself, typically appearing tan in color.
Next, a close inspection of the cluster center shows
several unusual and repeated galaxy shapes,
typically more blue.
These are multiple images of a few distant galaxies,
showing that the cluster is a
strong gravitational lens.
It is the relatively
weak distortions of the many distant
faint blue galaxies all over the image, however, that indicates the existence of the
dark matter ring.
The computationally modeled dark matter ring spans about five million
light years
and been digitally superimposed to the image in diffuse blue.
A hypothesis for the formation of the huge dark matter
ring holds that it is a transient feature formed when galaxy cluster CL0024+17 collided with another cluster of galaxies about one billion years ago,
leaving a ring similar to when a
rock is thrown in a pond.